1. Field of the Invention
The present invention relates generally to a sensor and more specifically to a sensor for measuring the length of filament, thread or the like drawn from a storage device.
2. Description of the Prior Art
A previously proposed sensor arrangement for a weaving loom is shown in FIG. 1 of the drawings. In this arrangement weft yarn y is wound onto a drum 2 by a winding arrangement 3 and retained thereon by a retaining device 4. During picking the retaining device 4 is actuated to retract a blocking member 5 from a recess 6 formed in the drum 2 and permit a number of loops of weft yarn y to be drawn axially off the drum.
The amount of yarn y stored on the drum is controlled by a first sensor 7 which directs a beam of light against the drum and which, in response to the amount of light reflected therefrom, induces suitable energization of the winding arrangement 3 in a manner to maintain a predetermined length of yarn on the drum. The amount of yarn permitted to be released from the drum 2 during each picking operation is controlled by a second sensor 8, which, like the first, directs a beam of light against the drum 2 in a manner that the passage of weft yarn y across the point where the beam impinges on the drum 2, induces a change in the amount of light reflected and thus the output of the light receiving section of the second sensor 8. A control unit 9 is responsive to the output of the second sensor 8 and controls the operation of the retaining device 4.
However, the latter mentioned sensor arrangement has suffered from the drawback that when applied to high speed weaving machines wherein weft yarns having a diameter ranging from tens of microns to hundreds of microns, are exposed to the beam of light for only a few micro seconds, accurate detection of each loop being drawn off the drum becomes extremely difficult. Non-detection of one of more loops of weft yarn y being drawn off the storage drum 4 of course invites an inevitable malfuction of the loom.
A full description of the above mentioned arrangement may be found in Japanese Patent Application first publication No. Sho 57-29640 or corresponding U.S. Pat. No. 4,407,336 issued in the name of Steiner on Oct. 4, 1983.